I dont think thats the way for me, since I want the ship to be also mounted by several other npcs (e.g. cannons) like this tank is mounted by a turret (and I would appreciate if someone told me how its done because I have no idea and I couldnt find a tutorial).
Thats not that big problem at all, at least it should not be. Some ships have NPC crew sailing on them, so there is some system enabling even this. But I don't know where and how is it being set. I only know that ID of NPC "crew" is also in gameobject_template, but I have no idea to what table it reffers.
If I just use the same model path (e.g. WorldEXPANSION02DOODADSShipsND_Icebreaker_ship_BG.M2) for both the npc and the gob, it should work, shouldnt it?
You might get some visual flickering bugs and might have issues with clicking on NPC vehicle to enter it. Some sort of invisible collision object would be far better, if you were able to make/get it.
But that wouldnt allow people to enter the ship's interior, would it?
Not necessarily, it would work for moving NPC version, so you can use in fact both ways together. Push-out aura would be active on NPC only while NPC is moving (when passenger is inside vehicle), and it would be deactivated while NPC is standing (and while collision gob is spawned).
About NPC being "mounted" on another NPC, I can't help you with this while I never really toyed with vehicles much. Btw, I found a little flaw in that SAI script - it might not work for vehicle with more than 1 passenger. For instance, if you have 2 people inside of vehicle and one leaves, but one still remains there... What will happen? I guess I know and its not what we wanted. Well, it seems it won't be that easy.